The present invention relates to an optical information recording and reproducing apparatus to record/reproduce information in/from an optical information recording medium by using a holography.
In these days, with a Blu-ray Disc (BD) standard and a High Definition Digital Versatile Disc (HD DVD) standard, optical discs having as large as 50 GB recording density can be produced on a commercial basis in a consumer use by using a blue-violet semiconductor laser.
In the future, it is desired that the optical disc has a large recording capacity such as HDD (Hard Disc Drive) having as large as 100 GB to 1 TB.
However, for a purpose of realizing the above-mentioned ultra-high density optical disc, a new storage technique is required such that it is different from an old trend using an existing high density technique that depends on making a wavelength shorter and the NA of an object lens higher.
On researching into a next-generation storage technique, a hologram recording technique has been taken notice of recording digital information by using the holography.
The hologram recording technique is that a signal light beam having information of page data modulated two-dimensionally by a spatial light modulator is superposed with a reference light beam inside a recording medium, and an interference fringe pattern occurs at this time to thereby arise a refraction index modulation inside the recording medium and then record information.
On reproducing information, the reference light beam used for the record is irradiated on the recording medium with the same reference light beam arranged. Consequently, a hologram recorded in the recording medium acts as a diffraction grating to generate a diffracted light. This diffracted light is reproduced as an identical light containing the recorded signal light beam and phase information.
A reproduced signal light beam is detected two-dimensionally at a high speed by using an optical detector such as CMOS, CCD, etc. The above-mentioned hologram recording is effective for recording and reproducing a large amount of information in a high speed, since two-dimensional information is recorded and reproduced simultaneously by using a single hologram and a plural number of page data can be overwritten on the same position.
JP-A-2004-272268 has proposed a hologram recording technique. This document discloses a so-called angle multiplexing recording system in which a signal light beam is converged onto an optical information recording medium by a lens, at the same time, the reference light beam of a parallel light beam is irradiated thereon so as to be made interfered with the signal light beam to record a hologram, and further, in order to execute a multiple recording, different page data is displayed on the spatial light modulator, while an incident angle of the reference light beam toward the optical recording medium is varied. JP-A-2004-272268 also discloses a technique in which the signal light beam is converged on the optical information recording medium by a lens to arrange an opening or aperture (spatial filter) on its light waist position, so that an interval adjacent to the hologram can be made short, and the recording density or capacity can be made increased, compared with the existing angle-multiplex-recording system.
WO2004-102542 has also proposed a hologram recording technique. This document discloses a technique using a shift multiplex system in which a light coming from an inner side of pixels is set to the signal light beam flux in a single spatial light modulator and a light coming from an outer side of orbicular zone pixels is set to the reference light beam therein. Both of the light beams are converged onto an optical recording medium by using the same lens so as to make the signal and reference light beams interfered at a vicinity of a lens focal plane to thereby record a hologram.
Further, JP-A-2007-101881 has disclosed that a fixing process is required for prior to a recording when optical information is recorded in an optical recording medium. In this case, the fixing process prior to the recording is referred to as a pre-cure process.
Further, JP-A-2007-256945 has disclosed that a fixing process is required after the recording when the optical information is recorded in the optical information recording medium. It says that a chemical reaction caused by a recording light beam occurs in the optical information recording medium and in the case of the chemical reaction caused by a reproduced illumination beam etc., too, a reproduction condition is unstable since the recorded information condition is changed a little bit at a time and recorded data may disappear, which is not desirable. Therefore, JP-A-2007-256945 says that fixing process is required so that the chemical reaction may not occur which otherwise occur due to the reproduced illumination beam etc., after the recording. JP-A-2007-256945 and JP-A-2007-519036 have also disclosed a technique for executing fixing process and recording process at the same time after recording to thereby shorten a time period involved by eliminating the need for separately allocating the time for the fixing process.